Giveaway - I need your help

So, as I said a few posts ago, I'm planning on doing a giveaway as a thankyou to everyone who has followed my blog! I really do appreciate it and love reading all your comments. A lot of people don't understand or 'get' my obesession with beauty products as it's just not their 'thing'. I think everyone has something they have a passion for and this is mine. It's nice to be able to blog about my interests, share it with you all and know that you will find what I have to say interesting and helpful (Or so I hope!).

Anyway, as I'm new to this whole blogging world I wondered if you could help. Basically, I want to know how I will choose the winner of my giveaway? This might sound SO stupid and it's probably really simple but I obviously want to choose the winner in a fair way? I've tried searching a few other blogs and I can't really figure out how they decide?

Also, while I'm on the topic of a giveaway, I'd love it if you could post in the comments below any suggestions you might have for prizes. I want to choose a prize that will suit most people and something that you would really like to try. Do you prefer make-up, skin care, hair care, nail polish, false tan or just a random mix of things?

I realise this is a pretty random post but I don't want to do my first ever Giveaway being completely clueless to how the whole process works!

Thanks Again for your help,